第 16 章 C 预处理器和 C 库（qsort() 函数）

 1 /*----------------------------------------
 2     qsorter.c -- 用 qsort() 排序一组数字
 3 ----------------------------------------*/
 4 
 5 #include <stdio.h>
 6 #include <stdlib.h>        //提供函数 rand() 原型
 7 
 8 #define NUM 40
 9 
10 void fillarray(double ar[], int n);
11 void showarray(const double ar[], int n);
12 int mycomp(const void *p1, const void *p2);
13 
14 int main()
15 {
16     double vals[NUM];
17 
18     fillarray(vals, NUM);
19     puts("Random list:");
20     showarray(vals, NUM);
21 
22     qsort(vals, NUM, sizeof(double), mycomp);
23     puts("\nSorted list:");
24     showarray(vals, NUM);
25 
26     return 0;
27 }
28 
29 void fillarray(double ar[], int n)
30 {
31     for (int index = 0; index != n; ++index)
32         ar[index] = (double)(rand()) / ((double)(rand()) + 0.1);
33 }
34 
35 void showarray(const double ar[], int n)
36 {
37     int index = 0;
38 
39     for (; index != n; ++index)
40     {
41         printf("%9.4f ", ar[index]);
42         if (index % 6 == 5) putchar('\n');
43     }
44 
45     if (index % 6 != 0) putchar('\n');
46 }
47 
48 int mycomp(const void *p1, const void *p2)
49 {
50     const double *a1 = (double*)p1;
51     const double *a2 = (double*)p2;
52 
53     if (*a1 > *a2)
54         return 1;
55     else if (*a1 == *a2)
56         return 0;
57     else
58         return -1;
59 }

qsorter.c